The present invention relates to the art of earth boring and, more particularly, to a raise bit for enlarging a first hole into a second hole having a larger diameter.
A relatively large diameter hole may be provided between a first location and a second location in a mine or other location by an operation commonly referred to as raise drilling. A raise drilling operation begins by drilling a small diameter pilot hole through the earth from a first location to an opening at the second location using a small diameter pilot bit. After the pilot hole is completed, the pilot bit is removed from the drill string and a large diameter raise bit attached. The raise bit is rotated and drawn along the pilot hole, thereby enlarging the pilot hole to the desired size. The hole thus formed may be further enlarged to a larger diameter hole by drawing a larger raise bit along said hole.
On many occasions, the hole to be enlarged extends to an area accessible only through a small drift or passage, and very little headroom is available for the raise bit. This creates difficulties when attempting to connect the raise bit to the drill string. It is, therefore, desirable to provide a raise bit that can be expanded to encompass a variety of large diameters without increasing the overall height of the bit. It is also desirable to provide a single raise bit that can be utilized to bore large diameter holes of various sizes. As shown in U.S. Pat. No. 3,659,659 to Carl L. Lichte, patented May 2, 1972, raise bits of the prior art generally include a bit body positioned about a central bit axis with rolling cutters mounted at various distances from the central bit axis for disintegrating the earth formations. The rolling cutters may be locked in place on the bit by various locking mechanisms. For example, locking mechanisms are shown in U.S. Pat. No. 3,203,492 to C. L. Lichte, patented Aug. 31, 1965; in U.S. Pat. No. 3,705,635 to William M. Conn patented Dec. 12, 1972; and in U.S. Pat. No. 3,612,196 to Robert L. Dixon patented Oct. 12, 1971. The cutters may be positioned to cut the working face according to various geometries. For example, cutter locations are shown in U.S. Pat. Re. No. 27,597 to M. L. Talbert patented Mar. 13, 1973, in U.S. Pat. No. 3,805,901 to William D. Coski, patented Apr. 23, 1974, and in U.S. Pat. No. 3,638,740 to Dan B. Justman, patented Feb. 1, 1972. A lubrication system may be provided to transmit lubricant to the bearings of the rolling cutters, as shown in U.S. Pat. No. 3,675,729 to William J. Neilson, patented July 11, 1972.